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Postretirement Benefit Plans (Net Periodic Benefit (Income) Costs) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Postretirement Health And Life Coverage [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 3 $ 3 $ 4
Interest cost 13 17 17
Amortization of prior service cost (25) (25) (25)
Amortization of net (gain) or loss   (5) (1)
Net periodic postretirement benefit (income) cost (9) (10) (5)
Director's Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 49 51 36
Interest cost 31 42 38
Amortization of prior service cost     22
Net periodic postretirement benefit (income) cost 80 93 $ 96
Scottdale Defined Benefit Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 79 92  
Interest cost 180 217  
Expected return on plan assets (273) (254)  
Recognized net actuarial gain   (59)  
Net periodic postretirement benefit (income) cost $ (14) $ (4)